The invention relates to a process for the selective oxidation of C3 to C5 alkanes and alkenes to their corresponding unsaturated carboxylic acids and unsaturated nitriles.
In virtually all catalytic processes, the stability, or useful lifetime, of a catalyst is critical to its economic viability in the process. In addition to activity and selectivity, catalysts that show extended lifetime benefits are highly preferred. In a cyclic fluid bed operation, a key economic factor is catalyst make-up rate, otherwise known as the rate of addition of fresh catalyst needed to maintain certain activity levels in the reactor. This make up rate is a key factor in the choice of catalyst for the process. In a fixed bed operation, typically long catalyst cycle times are desired for highest viability. Short cycle times require faster catalyst change-out resulting in economic penalties such as additional catalyst cost, down time to repack catalyst, and lost productivity.
In the oxidation of propylene or propane to acrylic acid, catalyst lifetime is a major factor in catalyst choice and process economics. Typically, catalyst lifetimes in the fixed bed commercial propylene-to-acrylic acid process are desired to reach at least 2 years in length, including any necessary catalyst regeneration steps. Extended catalyst lifetime is also desired for propane oxidation to acrylic acid as a similar fixed bed catalyst and process are used.
U.S. Pat. No. 7,553,986 discloses the staged oxygen intercondenser, hereinafter referred to as STOIC, process for oxidation of certain hydrocarbons, e.g. propane, to unsaturated carboxylic acids or unsaturated nitriles. Two- or three-stage processes may be used and show an advantage over single pass operation. Advantages stated are based on yield of acrylic acid.
It would be desirable to have a STOIC process operated under conditions capable of improving the useful life of the catalyst.